Image forming apparatus, image forming method, and method of producing printed material for generating a parallel line pattern of uniform concentration

ABSTRACT

An image forming apparatus includes: a pseudo-halftone processing unit that processes input image data to output image data of first resolution; a resolution converting unit that converts the image data of the first resolution into image data of second resolution that is higher than the first resolution; a modulation-signal generating unit that generates a modulation signal obtained by modulating the image data of the second resolution according to a clock signal; and a light-source driving unit that drives a light source according to the modulation signal. The pseudo-halftone processing unit converts a region of pixels having the same pixel value into a parallel line pattern that is formed with a plurality of parallel lines oblique relative to a direction of arrangement of pixels. The resolution converting unit generates the image data o in which each edge of the lines forming the parallel line pattern is smoothed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2013-099497 filedin Japan on May 9, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, an imageforming method, and a method of producing a printed material.

2. Description of the Related Art

Recently, digital printing machines applying an electrophotographicprocess are increasingly used in a production printing industry.Therefore, higher image quality and higher credibility are demanded ofthe digital printing machines applying the electrophotographic process.Particularly, improvement of uniformity in concentration of a halftoneis strongly demanded of the digital printing machines.

For the purpose of achieving high image quality, the digital printingmachines applying the electrophotographic process are equipped with animage processing unit that corrects image data by image processing. Thisimage processing unit performs the image processing with multiple-bitdata at high resolution of, for example, 1200 dots per inch (dpi) or2400 dpi.

Moreover, the digital printing machine applying the electrophotographicprocess includes a photosensitive drum a surface of which functions as aphotosensitive surface to be scanned, a light source that emits a laserbeam, a polygon mirror that deflects the laser beam from the lightsource, a scanning optical system that guides the laser beam deflectedby the polygon mirror to the surface of the photosensitive drum (surfaceto be scanned), and the like. The digital printing machine applying theelectrophotographic process modulates a beam emitted from the lightsource based on image data, and irradiates the beam from the lightsource on the surface to be scanned, to scan the surface to be scannedwith the beam, thereby forming an electrostatic latent image accordingto the image data on the photosensitive drum.

The digital printing machine applying the electrophotographic processhaving such a configuration uses a device that has multiple lightemitting points such as a laser diode array (LDA) and a vertical cavitysurface emitting laser (VCSEL). Thus, the digital printing machineapplying the electrophotographic process can form an electrostaticlatent image with resolution of, for example, 2400 dpi or 4800 dpi thatis higher than that of the image data at 1200 dpi.

Furthermore, in the digital printing machine, parallel line dithering inwhich a region having uniform concentration (that is, a region of pixelshaving the same pixel value) in image data is replaced with a parallelline pattern is performed in some cases as a pseudo-halftone processing.The parallel line pattern expresses concentration in surface by changingeach line width according to an original pixel value.

For example, in a technique described in Japanese Laid-open PatentPublication No. 2004-282344, resolution of a binary parallel linepattern generated by performing a pseudo-halftone processing in an imageprocessing unit is increased and then interpolation and smoothing areperformed, thereby suppressing roughness without changing the number oflines. In a technique disclosed in Japanese Patent No. 4026271, pixelsare divided by small regions and resolution thereof is increased, andsmoothing is performed on an edge portion of an image, to obtain highimage quality.

When an electrostatic latent image of a parallel line pattern is formedon a photosensitive drum, if a distances between lines is short, ashape, an electric-field intensity distribution, and the like of theelectrostatic latent image corresponding to one line are influenced byan adjacent electrostatic latent image. Particularly, if line intervalsare short, a low electric-field intensity area in which adhesion oftoner is unstable is generated. Therefore, in a digital printingmachine, when the parallel line dithering is performed, it is preferablethat the electric field intensity of a latent image of each line beequal to or higher than a threshold to keep a certain intensity at anyposition on the line, to make the concentration of an output imageuniform.

However, in a parallel line pattern of low-resolution image data, anedge of each line has a rough stepped-shape. Because of this, in aparallel line pattern of low-resolution image data, distances betweenlines vary depending on positions of the lines, and influence of alatent image corresponding to an adjacent line varies, and therefore, anarea in which the electric field intensity is partially low isgenerated. As a result, toner can adhere non-uniformly, or tonerscattering can occur between lines. Accordingly, for the digitalprinting machine, it has been difficult to obtain uniform concentrationwhen the parallel line dithering is performed on low-resolution imagedata.

To solve this problem, it is necessary to perform the parallel linedithering on higher-resolution image data in the digital printingmachine. However, if the parallel line dithering is performed onhigher-resolution image data, the amount of data to be transferred fromthe pseudo-halftone processing unit to a light-source driving circuitpositioned downstream increases, and thus limiting productivity.

In view of the above, there is a need to provide an image formingapparatus, an image forming method, and a method of producing a printedmaterial that can make concentration of a parallel line pattern uniform.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

An image forming apparatus forms an image according to light emittedfrom a light source. The image forming apparatus includes: apseudo-halftone processing unit that processes input image data tooutput image data of first resolution; a resolution converting unit thatconverts the image data of the first resolution into image data ofsecond resolution that is higher than the first resolution; amodulation-signal generating unit that generates a modulation signalobtained by modulating the image data of the second resolution accordingto a clock signal; and a light-source driving unit that drives the lightsource according to the modulation signal. The pseudo-halftoneprocessing unit converts a region of pixels having the same pixel valuein the input image data into a parallel line pattern that is formed witha plurality of parallel lines oblique relative to a direction ofarrangement of pixels to express concentration by an area ratio. Theresolution converting unit generates the image data of the secondresolution in which each edge of the lines forming the parallel linepattern is smoothed.

An image forming method forms an image according to light emitted from alight source. The image forming method includes: a pseudo-halftoneprocessing step of processing input image data to output image data offirst resolution; a resolution converting step of converting the imagedata of the first resolution into image data of second resolution thatis higher than the first resolution; a modulation-signal generating stepof generating a modulation signal obtained by modulating the image dataof the second resolution according to a clock signal; and a light-sourcedriving step of driving the light source according to the modulationsignal. At the pseudo-halftone processing step, a region of pixelshaving the same pixel value in the input image data is converted into aparallel line pattern that is formed with a plurality of parallel linesoblique relative to a direction of arrangement of pixels to expressconcentration by an area ratio. At the resolution converting step, theimage data of the second resolution in which each edge of the linesforming the parallel line pattern is smoothed is generated.

A method produces a printed material. The method includes: apseudo-halftone processing step of processing input image data to outputimage data of first resolution; a resolution converting step ofconverting the image data of the first resolution into image data ofsecond resolution that is higher than the first resolution; amodulation-signal generating step of generating a modulation signalobtained by modulating the image data of the second resolution accordingto a clock signal; an electrostatic-latent-image forming step offorming, on a latent image carrier, an electrostatic latent image bylight emitted from a light source by driving the light source accordingto the modulation signal; an adhesion step of making toner adhere to theelectrostatic latent image that is formed on the latent image carrier;and a transfer step of transferring the toner onto an object to producea printed material. At the pseudo-halftone processing step, a region ofpixels having the same pixel value in the input image data is convertedinto a parallel line pattern that is formed with a plurality of parallellines oblique relative to a direction of arrangement of pixels toexpress concentration by an area ratio. At the resolution convertingstep, the image data of the second resolution in which each edge of thelines forming the parallel line pattern is smoothed is generated.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a color printer 2000according to an embodiment;

FIG. 2 is a diagram showing an example of arrangement of optical sensors2245 a 2245 b, 2245 c;

FIG. 3 is a configuration diagram of the optical sensors 2245 a 2245 b,2245 c;

FIG. 4 is a configuration diagram of an optical system of an opticalscanning device 2010;

FIG. 5 is a diagram showing an example of an optical path from a lightsource 2200 a to a polygon mirror 2104 and an optical path from a lightsource 2200 b to the polygon mirror 2104;

FIG. 6 is a diagram showing an example of an optical path from a lightsource 2200 c to the polygon mirror 2104 and an optical path from alight source 2200 d to the polygon mirror 2104;

FIG. 7 is a diagram showing an example of optical paths from the polygonmirror 2104 to respective photosensitive drums 2030;

FIG. 8 is a configuration diagram of an electric system of the opticalscanning device 2010;

FIG. 9 is a configuration diagram of an interface unit 3101;

FIG. 10 is a configuration diagram of an image processing unit 3102;

FIG. 11 is a diagram showing an example of a parallel line pattern thatis generated by a pseudo-halftone processing unit 3224;

FIG. 12 is a configuration diagram of a drive control unit 3103;

FIG. 13 is a configuration diagram of a resolution converting unit 3231;

FIG. 14 is a diagram showing a part of a parallel line pattern in imagedata of 1200 dpi;

FIG. 15 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth an upper edge of a line shown in FIG. 14;

FIG. 16 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth a lower edge of the line shown in FIG. 14;

FIG. 17 is a diagram showing a part of a parallel line pattern in imagedata of 4800 dpi after edges of the lines shown in FIG. 14 have beensmoothed;

FIG. 18 is a configuration diagram of the resolution converting unit3231 according to a first modification;

FIG. 19 is a configuration diagram of the resolution converting unit3231 according to a second modification;

FIG. 20 is a diagram showing a part of a parallel line pattern in imagedata of 1200 dpi that is formed with 45-degree lines;

FIG. 21 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth an upper edge of a line shown in FIG. 20;

FIG. 22 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth a lower edge of the line shown in FIG. 20;

FIG. 23 is a diagram showing a part of a parallel line pattern in imagedata of 4800 dpi after edges of the lines shown in FIG. 20 have beensmoothed;

FIG. 24 is a configuration diagram of the resolution converting unit3231 according to a third modification;

FIG. 25 is a diagram showing a part of a parallel line pattern of 1200dpi expressed by ternary pixel values;

FIG. 26 is a diagram showing a first example of an edge pattern and asmooth pattern to detect and smooth an upper edge of a line shown inFIG. 25;

FIG. 27 is a diagram showing a second example of the edge pattern andthe smooth pattern to detect and smooth an upper edge of the line shownin FIG. 25;

FIG. 28 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth a lower edge of the line shown in FIG. 25;and

FIG. 29 is a diagram showing a part of a parallel line pattern in imagedata of 4800 dpi after edges of the lines shown in FIG. 25 have beensmoothed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A color printer 2000 is explained in detail as an example of an imageforming apparatus that is an embodiment of the present invention withreference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of the color printer 2000according to the embodiment. The color printer 2000 produces a printedmaterial by transferring toner onto recording paper (object). The colorprinter 2000 is a tandem-system multi-color printer that forms afull-color image by superimposing four colors (black, cyan, magenta, andyellow).

The color printer 2000 includes an optical scanning device 2010, fourunits of photosensitive drums 2030 a, 2030 b, 2030 c, 2030 d (describedas photosensitive drum 2030 when the four units are collectivelydescribed), four units of cleaning units 2031 a, 2031 b, 2031 c, 2031 d(described as cleaning unit 2031 when the four units are collectivelydescribed), and four units of charge devices 2032 a, 2032 b, 2032 c,2032 d (described as charge device 2032 when the four units arecollectively described). Furthermore, the color printer 2000 includesfour units of developing rollers 2033 a, 2033 b, 2033 c, 2033 d(described as developing roller 2033 when the four units arecollectively described), four units of toner cartridges 2034 a, 2034 b,2034 c, 2034 d (described as toner cartridge 2034 when the four unitsare collectively described). Moreover, the color printer 2000 includes atransfer belt 2040, a transfer roller 2042, a fixing roller 2050, apaper feeding roller 2054, a registration roller pair 2056, a paperejection roller 2058, a paper feeding tray 2060, a paper ejection tray2070, a communication control device 2280, a concentration detector2245, four units of home position sensors 2246 a, 2246 b, 2246 c, 2246 d(described as home position sensor 2246 when the four units arecollectively described), and a printer control device 2090.

The communication control device 2080 controls interactive communicationwith a higher-order device (for example, a computer) through a networkand the like.

The printer control device 2090 performs overall control of therespective components equipped in the color printer 2000. The printercontrol device 2090 includes a central processing unit (CPU), aread-only memory (ROM) in which a program that is described in a codeused by the CPU and various kinds of data that are used when the programis executed, a random access memory (RAM) that is a memory foroperation, an analog-to-digital (A/D) converter circuit that convertsanalog data to digital data, and the like. The printer control device2090 controls the respective components according to a request from ahigher-order device, and transmits image data received from ahigher-order device to the optical scanning device 2010.

The photosensitive drum 2030 a, the charge device 2032 a, the developingroller 2033 a, the toner cartridge 2034 a, and the cleaning unit 2031 aare used in a group. These units form an image forming station thatforms black images (also called K station).

The photosensitive drum 2030 b, the charge device 2032 b, the developingroller 2033 b, the toner cartridge 2034 b, and the cleaning unit 2031 bare used in a group. These units form an image forming station thatforms cyan images (also called C station).

The photosensitive drum 2030 c, the charge device 2032 c, the developingroller 2033 c, the toner cartridge 2034 c, and the cleaning unit 2031 care used in a group. These units form an image forming station thatforms magenta images (also called M station).

The photosensitive drum 2030 d, the charge device 2032 d, the developingroller 2033 d, the toner cartridge 2034 d, and the cleaning unit 2031 dare used in a group, and forms an image forming station that formsyellow images (also called Y station).

Each of the photosensitive drums 2030 is an example of a latent imagecarrier and has a photosensitive layer on a surface thereof. That is,the surface of each of the photosensitive drums 2030 is a surface to bescanned. The photosensitive drums 2030 a, 2030 b, 2030 c, 2030 d arearranged such that rotation axes are aligned parallel, and for example,rotated all in an identical direction (for example, a direction of anarrow in the plane of FIG. 1).

In the explanation herein, in a three-dimensional orthogonal coordinatesystem, a direction parallel to a center axis of each of thephotosensitive drums 2030 is a Y-axis direction, and a direction along adirection of alignment of the respective photosensitive drums 2030 is anX-axis direction.

Each of the charge devices 2032 uniformly charges the surface of thecorresponding photosensitive drums 2030. The optical scanning device2010 irradiates beams that are modulated for respective colors based onimage data (black image data, cyan image data, magenta image data, andyellow image data) to the charged surfaces of the correspondingphotosensitive drums 2030. Thus, on the surfaces of the respectivephotosensitive drums 2030, only a part on which light is irradiatedloses an electric charge, and latent images corresponding to the imagedata are formed on the surfaces of the respective photosensitive drums2030. The latent images formed herein are transferred toward a directionof the corresponding developing rollers 2033 with rotation of thephotosensitive drums 2030. A configuration of the optical scanningdevice 2010 is described in detail later.

On each of the photosensitive drums 2030, an area in which image data iswritten is called an “effective scanning area”, an “image forming area”,an “effective image area”, or the like.

In the toner cartridge 2034 a, black toner is stored, and the blacktoner is supplied to the developing roller 2033 a. In the tonercartridge 2034 b, cyan toner is stored, and the cyan toner is suppliedto the developing roller 2033 b. In the toner cartridge 2034 c, magentatoner is stored, and the magenta toner is supplied to the developingroller 2033 c. In the toner cartridge 2034 d, yellow toner is stored,and the yellow toner is supplied to the developing roller 2033 d.

To each of the developing rollers 2033, toner from a corresponding tonercartridge 2034 is thinly and uniformly applied on the surface withrotation. When the toner on the surface of each of the developingrollers 2033 touches the surface of the corresponding photosensitivedrum 2030, the toner is transferred only to the part on which light hasbeen irradiated on the surface, and adheres thereto. That is, each ofthe developing rollers 2033 makes toner adhere to a latent image formedon the surface of the corresponding photosensitive drum 2030 to make theimage appear.

The transfer belt 2040 is arranged around a belt rotating mechanism, androtates in a predetermined direction. An outer surface of the transferbelt 2040 comes into contact with the surface of each of thephotosensitive drums 2030 a, 2030 b, 2030 c, 2030 d, at a positionopposite to the optical scanning device 2010. Moreover, the transferbelt 2040 comes into contact with the transfer roller 2042 at the outersurface thereof.

The images (toner images) to which toner has adhered on the surfaces ofthe respective photosensitive drums 2030 are transferred toward adirection of the transfer belt 2040 with rotation of the photosensitivedrums 2030. The respective toner images of yellow, magenta, cyan, andblack are sequentially transferred onto the transfer belt 2040 atpredetermined timing to be superimposed, to form a color image. Thecolor image formed on the transfer belt 2040 moves toward a direction ofthe transfer roller 2042 as the transfer belt 2040 moves.

In the paper feeding tray 2060, recording paper is stored. The paperfeeding roller 2054 is arranged near the paper feeding tray 2060, andthe paper feeding roller 2054 takes out the recording paper one by onefrom the paper feeding tray 2060, and conveys to the registration rollerpair 2056.

The registration roller pair 2056 sends the recording paper into a gapbetween the transfer belt 2040 and the transfer roller 2042 atpredetermined timing. Thus, the color image on the transfer belt 2040 istransferred onto the recording paper. The recording paper to which theimage has been transferred is sent to the fixing roller 2050.

The fixing roller 2050 applies heat and pressure to the recording paper,and thus the toner is fixed onto the recording paper. The recordingpaper on which the toner is thus fixed is sent to the paper ejectiontray 2070 through the paper ejection roller 2058, and is sequentiallystacked on the paper ejection tray 2070.

Each of the cleaning units 2031 removes toner (residual toner) remainingon the surface of the corresponding photosensitive drum 2030. Thesurface of the photosensitive drum 2030 from which the residual tonerhas been removed returns to a position opposing to the correspondingcharge device 2032 again.

A concentration detector 2245 is arranged on a −X side of the transferbelt 2040 (a position on an upstream side in a direction of travel ofthe transfer belt 2040 relative to the fixing roller 2050, and on adownstream side relative to the four units of the photosensitive drums2030). The concentration detector 2245 includes three optical sensors2245 a, 2245 b, and 2245 c as shown in FIG. 2 as an example.

The optical sensor 2245 a is arranged at a position opposing to aportion adjacent to a −Y side end (one end side in a direction of widthof the transfer belt 2040) in the effective image area on the transferbelt 2040. The optical sensor 2245 c is arranged at a position opposingto a portion adjacent to a +Y side end (the other end in the directionof width of the transfer belt 2040) in the effective image area on thetransfer belt 2040. The optical sensor 2245 b is arranged at anapproximately center (a center position in the direction of width of thetransfer belt 2040) between the optical sensor 2245 a and the opticalsensor 2245 c relative to a main scanning direction. Herein, a centerposition of the optical sensor 2254 a is Y1, a center position of theoptical sensor 2245 b is Y2, and a center position of the optical sensor2245 c is Y3 relative to the main scanning direction (Y-axis direction).

Each of the optical sensors 2245 a, 2245 b, 2245 c has a light-emittingdiode (LED) 11 that emits light (hereinafter, described also as“detection light”) toward the transfer belt 2040, aspecular-reflection-light receiving element 12 that receives specularreflection light from the transfer belt 2040 or a toner pad on thetransfer belt 2040, a diffused-reflection-light receiving element 13that receives diffused reflection light from the transfer belt 2040 or atoner pad on the transfer belt 2040 as shown in FIG. 3 as an example.Each of the light receiving elements outputs a signal (photoelectricalconversion signal) according to an amount of received light.

The home position sensor 2246 a detects a home position in rotation ofthe photosensitive drum 2030 a. The home position sensor 2246 b detectsa home position in rotation of the photosensitive drum 2030 b. The homeposition sensor 2246 c detects a home position in rotation of thephotosensitive drum 2030 c. The home position sensor 2246 d detects ahome position in rotation of the photosensitive drum 2030 d.

FIG. 4 is a configuration diagram of an optical system the opticalscanning device 2010. FIG. 5 is a diagram showing an example of anoptical path from a light source 2200 a to a polygon mirror 2104 and anoptical path from a light source 2200 b to the polygon mirror 2104. FIG.6 is a diagram showing an example of an optical path from a light source2200 c to the polygon mirror 2104 and an optical path from a lightsource 2200 d to the polygon mirror 2104. FIG. 7 is a diagram showing anexample of optical paths from the polygon mirror 2104 to the respectivephotosensitive drums 2030.

Next, a configuration of the optical system of the optical scanningdevice 2010 is explained. The optical scanning device 2010 includes fourunits of the light sources 2200 a, 2200 b, 2200 c, 2200 d, four units ofcoupling lenses 2201 a, 2201 b, 2201 c, 2201 d, four units of openingplates 2202 a, 2202 b, 2202 c, 2202 d, and four units of cylindricallenses 2204 a, 2204 b, 2204 c, 2204 d as the optical system.Furthermore, the optical scanning device 2010 includes the polygonmirror 2104, four units of scanning lenses 2105 a, 2105 b, 2105 c, 2105d, six pieces of fold back mirrors 2106 a, 2106 b, 2106 c, 2106 d, 2108b, 2108 c as the optical system. These components are assembled atpredetermined positions in an optical housing.

Moreover, the optical scanning device 2010 also has a circuit of anelectric system, and the circuit of the electric system is explained inFIG. 8 and later.

Each of the light sources 2200 a, 2200 b, 2200 c, 2200 d includes asurface-emitting laser array in which multiple light emitting units aretwo-dimensionally arranged. The light emitting units of thesurface-emitting laser array are arranged such that the intervalsbetween the light emitting units are equal when all of the lightemitting units orthogonally project on a virtual line that extends in asub-scanning support direction. Each of the light sources 2200 a, 2200b, 2200 c, 2200 d is a VCSEL, as an example.

The coupling lens 2201 a is arranged on an optical path of the beamemitted from the light source 2200 a, and converts the beam passingtherethrough into an approximately parallel beam. The coupling lens 2201b is arranged on an optical path of the beam emitted from the lightsource 2200 b, and converts the beam passing therethrough into anapproximately parallel beam. The coupling lens 2201 c is arranged on anoptical path of the beam emitted from the light source 2200 c, andconverts the beam passing therethrough into an approximately parallelbeam. The coupling lens 2201 d is arranged on an optical path of thebeam emitted from the light source 2200 d, and converts the beam passingtherethrough into an approximately parallel beam.

The opening plate 2202 a has an opening, and shapes the beam through thecoupling lens 2201 a. The opening plate 2202 b has an opening, andshapes the beam through the coupling lens 2201 b. The opening plate 2202c has an opening, and shapes the beam through the coupling lens 2201 c.The opening plate 2202 d has an opening, and shapes the beam through thecoupling lens 2201 d.

The cylindrical lens 2204 a makes the beam that has passed through theopening of the opening plate 2202 a form an image near a deflectionreflection surface of the polygon mirror 2104 relative to a Z-axisdirection. The cylindrical lens 2204 b makes the beam that has passedthrough the opening of the opening plate 2202 b form an image near thedeflection reflection surface of the polygon mirror 2104 relative to theZ-axis direction. The cylindrical lens 2204 c makes the beam that haspassed through the opening of the opening plate 2202 c form an imagenear the deflection reflection surface of the polygon mirror 2104relative to the Z-axis direction. The cylindrical lens 2204 d makes thebeam that has passed through the opening of the opening plate 2202 dform an image near the deflection reflection surface of the polygonmirror 2104 relative to the Z-axis direction.

An optical system constituted of the coupling lens 2201 a, the openingplate 2202 a, and the cylindrical lens 2204 a is a pre-deflector opticalsystem of the K station. An optical system constituted of the couplinglens 2201 b, the opening plate 2202 b, and the cylindrical lens 2204 bis a pre-deflector optical system of the C station. An optical systemconstituted of the coupling lens 2201 c, the opening plate 2202 c, andthe cylindrical lens 2204 c is a pre-deflector optical system of the Mstation. An optical system constituted of the coupling lens 2201 d, theopening plate 2202 d, and the cylindrical lens 2204 d is a pre-deflectoroptical system of the Y station.

The polygon mirror 2104 has a four-sided mirror having a two-stagestructure that rotates about an axis parallel to the Z axis, and eachmirror functions as a deflection reflection surface. It is arranged suchthat each of the beam from the cylindrical lens 2204 b and the beam fromthe cylindrical lens 2204 c is deflected at the four-sided mirror at afirst stage (lower stage), and each of the beam from the cylindricallens 2204 a and the beam from the cylindrical lens 2204 d is deflectedat the four-sided mirror at a second stage (upper stage).

Moreover, each of the beams from the cylindrical lens 2204 a and thecylindrical lens 2204 b is deflected toward the −X side of the polygonmirror 2104, and each of the beams from the cylindrical lens 2204 c andthe cylindrical lens 2204 d is deflected toward a +X side of the polygonmirror 2104.

Each of the scanning lenses 2105 a, 2105 b, 2105 c, 2105 d has anoptical power to collect beams near the corresponding photosensitivedrum 2030, and an optical power that a light spot moves in the mainscanning direction at a constant speed on a surface of the correspondingphotosensitive drum 2030 with rotation of the polygon mirror 2104.

The scanning lens 2105 a and the scanning lens 2105 b are arranged onthe −X side of the polygon mirror 2104, and the scanning lens 2105 c andthe scanning lens 2105 d are arranged on the +X side of the polygonmirror 2104.

The scanning lens 2105 a and the scanning lens 2105 b are layered in theZ-axis direction. The scanning lens 2105 b is opposed to the four-sidedmirror at the first stage. The scanning lens 2105 a is opposed to thefour-sided mirror at the second stage.

Furthermore, the scanning lens 2105 c and the scanning lens 2105 d arelayered in the Z-axis direction. The scanning lens 2105 c is opposed tothe four-sided mirror at the first stage. The scanning lens 2105 d isopposed to the four-sided mirror at the second stage.

The beam from the cylindrical lens 2204 a deflected by the polygonmirror 2104 is irradiated to the photosensitive drum 2030 a through thescanning lens 2105 a and the fold back mirror 2106 a, to form a lightspot. This light spot moves in the direction of length of thephotosensitive drum 2030 a with rotation of the polygon mirror 2104.That is, this light spot scans on the photosensitive drum 2030 a. Thedirection of movement of this light spot at this time is the “mainscanning direction” at the photosensitive drum 2030 a, and the directionof rotation of the photosensitive drum 2030 a is the “sub-scanningdirection” at the photosensitive drum 2030 a.

Moreover, the beam from the cylindrical lens 2204 b deflected by thepolygon mirror 2104 is irradiated to the photosensitive drum 2030 bthrough the scanning lens 2105 b, the fold back mirror 2106 b, and thefold back mirror 2108 b, to form a light spot. This light spot moves inthe direction of length of the photosensitive drum 2030 b with rotationof the polygon mirror 2104. That is, this light spot scans on thephotosensitive drum 2030 b. The direction of movement of this light spotat this time is the “main scanning direction” at the photosensitive drum2030 b, and the direction of rotation of the photosensitive drum 2030 bis the “sub-scanning direction” at the photosensitive drum 2030 b.

Furthermore, the beam from the cylindrical lens 2204 c deflected by thepolygon mirror 2104 is irradiated to the photosensitive drum 2030 cthrough the scanning lens 2105 c, the fold back mirror 2106 c, and thefold back mirror 2108 c, to form a light spot. This light spot moves inthe direction of length of the photosensitive drum 2030 c with rotationof the polygon mirror 2104. That is, this light spot scans on thephotosensitive drum 2030 c. The direction of movement of this light spotat this time is the “main scanning direction” at the photosensitive drum2030 c, and the direction of rotation of the photosensitive drum 2030 cis the “sub-scanning direction” at the photosensitive drum 2030 c.

Moreover, the beam from the cylindrical lens 2204 d deflected by thepolygon mirror 2104 is irradiated to the photosensitive drum 2030 dthrough the scanning lens 2105 d and the fold back mirror 2106 d, toform a light spot. This light spot moves in the direction of length ofthe photosensitive drum 2030 d with rotation of the polygon mirror 2104.That is, this light spot scans on the photosensitive drum 2030 d. Thedirection of movement of this light spot at this time is the “mainscanning direction” at the photosensitive drum 2030 d, and the directionof rotation of the photosensitive drum 2030 d is the “sub-scanningdirection” at the photosensitive drum 2030 d.

The respective fold back mirrors 2106 a, 2106 b, 2106 c, 2106 d, 2108 b,2108 c are arranged such that the respective optical path lengths to therespective photosensitive drums 2030 from the polygon mirror 2104 areidentical to each other, and such that incident positions and incidentangles of beams at the respective photosensitive drums 2030 areidentical to each other.

The optical system arranged on the optical path between the polygonmirror 2104 and each of the photosensitive drums 2030 is also called ascanning optical system. In this example, the scanning optical system ofthe K station is constituted of the scanning lens 2105 a and the foldback mirror 2106 a. Moreover, the scanning optical system of the Cstation is constituted of the scanning lens 2105 b and two pieces of thefold back mirrors 2106 b, 2108 b. Further, the scanning optical systemof the M station is constituted of the scanning lens 2105 c and twopieces of the fold back mirrors 2106 c, 2108 c. Furthermore, thescanning optical system of the Y station is constituted of the scanninglens 2105 d and the fold back mirror 2106 d. In each of the scanningoptical systems, the scanning lens 2105 may be configured with more thanone lens.

FIG. 8 is a configuration diagram of the electric system of the opticalscanning device 2010. The optical scanning device 2010 includes aninterface unit 3101, an image processing unit 3102, and a drive controlunit 3103, as components of the electric system.

The interface unit 3101 acquires image data that has been transferredfrom a higher-order device (for example, a computer), from the printercontrol device 2090. The interface unit 3101 then transfers the acquiredimage data to the image processing unit 3102 positioned at a subsequentstage.

In this example, the interface unit 3101 acquires 8-bit RGB image datahaving resolution of 1200 dpi and transfers the data to the imageprocessing unit 3102.

The image processing unit 3102 acquires image data from the interfaceunit 3101, and converts the image data into color image data that iscompatible with the printing mode. As an example, the image processingunit 3102 converts RGB image data into image data in a tandem format(CMYK format). Furthermore, the image processing unit 3102 performsvarious kinds of image processing in addition to the conversion of dataformat.

In this example, the image processing unit 3102 outputs 2-bit CMYK imagedata having resolution of 1200 dpi. The resolution of image data outputfrom the image processing unit 3102 is not limited to 1200 dpi, and anyresolution is applicable. Moreover, the resolution of image data outputfrom the image processing unit 3102 is referred to as first resolution.

The drive control unit 3103 acquires the image data of the firstresolution from the image processing unit 3102, and converts the imagedata into color image data of second resolution corresponding to drivingof the light source. The second resolution is higher than the firstresolution. In this example, the drive control unit 3103 converts into1-bit CMYK image data having resolution of 4800 dpi.

Furthermore, the drive control unit 3103 modulates the image data to aclock signal that indicates the light emission timing for a pixel, togenerate an independent modulation signal for each color. The drivecontrol unit 3103 drives the light sources 2200 a, 2200 b, 2200 c, 2200d according to the modulation signal corresponding to each color to emitlight.

Moreover, the drive control unit 3103 is an integrated circuit (IC) thatis formed into one chip and is arranged near the light sources 2200 a,2200 b, 2200 c, 2200 d as an example. The image processing unit 3102 andthe interface unit 3101 are arranged at positions farther than the lightsources 2200 a, 2200 b, 2200 c, 2200 d with respect to the drive controlunit 3103. The image-processing unit 3102 and the drive control unit3103 are connected by a cable 3104 therebetween.

The optical scanning device 2010 having such a configuration can makethe light sources 2200 a, 2200 b, 2200 c, 2200 d emit light according toimage data to form a latent image.

FIG. 9 is a configuration diagram of the interface unit 3101. Theinterface unit 3101 includes a flash memory 3211, a RAM 3212, aninterface (IF) circuit 3213, and a CPU 3214 as an example. The flashmemory 3211, the RAM 3212, the IF circuit 3213, and the CPU 3214 areconnected through a bus with each other.

In the flash memory 3211, programs that are executed by the CPU 3214 andvarious kinds of data that is required for execution of the programs bythe CPU 3214 are stored. The RAM 3212 is a memory area for operationwhen the CPU 3214 executes programs. The IF circuit 3213 interactivelycommunicates with the printer control device 2090.

The CPU 3210 operates according to a program stored in the flash memory3211, and controls the entire optical scanning device 2010. Theinterface unit 3101 having such a configuration transfers image data(RGB, 1200 dpi, 8 bits) that has been transmitted from the printercontrol device 2090 to the image processing unit 3102.

FIG. 10 is a configuration diagram of the image processing unit 3102.The image processing unit 3102 includes a color converting unit 3221, ablack generating unit 3222, a γ correction unit 3223, and apseudo-halftone processing unit 3224.

The color converting unit 3221 converts 8-bit RGB image data into 8-bitCMY image data. The black generating unit 3222 generates blackcomponents from the CMY image data that has been generated by the colorconverting unit 3221, to generate CMYK image data. The γ correction unit3223 performs linear conversion on levels of each color using a tableand the like.

The pseudo-halftone processing unit 3224 receives 8-bit image data(input image data) from the γ correction unit 3223. The pseudo-halftoneprocessing unit 3224 reduces the number of tones of the received 8-bitimage data to output 2-bit image data. The pseudo-halftone processingunit 3224 reduces the number of tones of the received 8-bit image datato 2 bits, for example, by performing a halftone processing bydithering, error diffusion processing, and the like.

The image processing unit 3102 as above outputs 2-bit CMYK image data ofthe first resolution (for example, 1200 dpi) to the drive control unit3103. The image processing unit 3102 may be implemented by hardwarepartially or entirely, or may be implemented by executing a softwareprogram by the CPU.

FIG. 11 is a diagram showing an example of a parallel line pattern thatis generated by the pseudo-halftone processing unit 3224. Thepseudo-halftone processing unit 3224 performs parallel line dithering asone of the halftone processing to reduce the number of tones. That is,the pseudo-halftone processing unit 3224 converts a region of pixelshaving the same pixel value in the received 8-bit image data into aparallel line pattern that is formed with multiple parallel linesoblique relative to the direction of arrangement of pixels, and therebyexpress the concentration by an area ratio.

In this case, the pseudo-halftone processing unit 3224 converts a regionof pixels having the same pixel value into a parallel line pattern thatis formed with multiple lines at an area ratio according to the pixelvalue. Thus, the pseudo-halftone processing unit 3224 can generate imagedata in which the concentration of the original image area is expressedby the area ratio.

The pseudo-halftone processing unit 3224 generates a parallel linepattern that is formed with multiple lines of the predetermined number(number of lines) per unit length. In this case, the pseudo-halftoneprocessing unit 3224 changes the width of each line according to theoriginal pixel value. Specifically, the pseudo-halftone processing unit3224 makes the width of lines smaller as a pixel value is smaller, andmakes the width of lines larger as a pixel is larger, as shown in FIG.11. Thus, the pseudo-halftone processing unit 3224 can form lines at anarea ratio according to a pixel value.

Alternatively, the pseudo-halftone processing unit 3224 may change thenumber of lines according to a set value. Moreover, the pseudo-halftoneprocessing unit 3224 sets an angle (screen angle) of lines that form aparallel line pattern relative to the direction of arrangement of pixelsto an angle according to a set value.

Moreover, the pseudo-halftone processing unit 3224 generates a parallelline pattern in which lines are drawn in binary, as an example. In thiscase, the pseudo-halftone processing unit 3224 uses a black value (valuecorresponding to 100% intensity of light emitted from the light source2200) for pixels forming the lines, and a white value (valuecorresponding to 0% intensity of light emitted from the light source2200) for pixels of a portion other than the lines.

Moreover, the pseudo-halftone processing unit 3224 may generate aparallel line pattern in which lines are drawn in ternary or more, as anexample. In this case, the pseudo-halftone processing unit 3224 uses ablack value (value corresponding to 100% intensity of light emitted fromthe light source 2200) for pixels forming a center portion of the lines,an intermediate value (for example, value corresponding to 50% intensityof light emitted from the light source 2200) for pixels forming a partof edges of the lines, and a white value (value corresponding to 0%intensity of light emitted from the light source 2200) for pixelsforming a portion other than the lines.

FIG. 12 is a configuration diagram of the drive control unit 3103. Thedrive control unit 3103 includes a resolution converting unit 3231, aclock generating unit 3232, a modulation-signal generating unit 3233,and a light-source driving unit 3234.

The resolution converting unit 3231 acquires image data of the firstresolution from the image processing unit 3102, and converts the imagedata into image data of the second resolution that is higher than thefirst resolution. In this example, the resolution converting unit 3231converts 2-bit CMYK image data of 1200 dpi into 1-bit CMYK image data of4800 dpi, and also reduces the number of tones at the same time with theconversion of resolution. As long as the processing to convert imagedata of resolution N (N is a positive integer) into image data ofresolution m×N (m is a positive integer equal to or larger than 2) isperformed, the resolution converting unit 3231 may perform conversioninto image data of any tone.

Furthermore, the resolution converting unit 3231 performs smoothing oneach of edges of lines in a parallel line pattern in the image data ofthe first resolution. The edges of lines signify side ends of astrip-shaped line. Smoothing edges is to make the shapes of the sideends smooth along the direction of extension of lines. The resolutionconverting unit 3231 outputs the image data of the second resolution inwhich each edge of the lines in the parallel line pattern are smoothed.

The clock generating unit 3232 generates a clock signal that indicateslight emission timing for a pixel. The clock signal can bephase-modulated at the resolution of ⅛ clock, for example.

The modulation-signal generating unit 3233 modulates image data for eachcolor according to the clock signal, and generates an independentmodulation signal for each color. In this example, the modulation-signalgenerating unit 3233 generates a modulation signal for each color of C,M, Y, and K. Furthermore, the modulation-signal generating unit 3233modulates image data into a clock signal for each color, insynchronization with write start timing based on the rotation positionof the photosensitive drums 2030. The modulation-signal generating unit3233 supplies the modulation signal independent for each color to thelight-source driving unit 3234.

The light-source driving unit 3234 drives the corresponding lightsources 2200 a, 2200 b, 2200 c, 2200 d according to each of themodulation signal independent for each color output from themodulation-signal generating unit 3233. Thereby, the light-sourcedriving unit 3234 can make each of the light sources 2200 a, 2200 b,2200 c, 2200 d emit light with the amount of light according to themodulation signal.

FIG. 13 is a configuration diagram of the resolution converting unit3231. The resolution converting unit 3231 has a line-region detectingunit 3241, an edge-pattern storage unit 3242, an edge detecting unit3243, a resolution increasing unit 3244, a demultiplexer 3245, asmooth-pattern storage unit 3246, a smoothing unit 3247, and amultiplexer 3248.

The line-region detecting unit 3241 acquires image data of the firstresolution from the image processing unit 3102, and detects a parallelline pattern in the image data of the first resolution. The line-regiondetecting unit 3241 then outputs a signal indicating a position of thedetected parallel line pattern in the image data of the firstresolution.

The line-region detecting unit 3241 detects a parallel line pattern byanalyzing a pattern of an image, as an example. Moreover, theline-region detecting unit 3241 may detect a parallel line pattern byreceiving data indicating a region at which the parallel line ditheringhas been performed, from the image processing unit 3102, as an example.

The edge-pattern storage unit 3242 stores edge patterns. An edge patternis a partial image of the first resolution (1200 dpi) that expresses astepped-shape of an edge of a line of the first resolution.

The edge detecting unit 3243 acquires image data of the first resolutionfrom the image processing unit 3102, the signal indicating a position ofa detected parallel line pattern from the line-region detecting unit3241, and the edge pattern of the first resolution (1200 dpi) from theedge-pattern storage unit 3242.

The edge detecting unit 3243 detects an edge region that matches withthe edge pattern of the first resolution from the parallel line patternin the image data of the first resolution, by pattern matching. The edgedetecting unit 3243 then outputs a signal indicating the position of theedge region.

The resolution increasing unit 3244 acquires the image data of the firstresolution from the image processing unit 3102. The resolutionincreasing unit 3244 increases the resolution of the image data of thefirst resolution to convert into image data of the second resolution. Inthis case, the resolution increasing unit 3244 also reduces the numberof tones by performing conversion from one dot at 1200 dpi expressed bya 2-bit tone into four dots in a horizontal direction at 4800 dpiexpressed by a 1-bit tone, as an example.

The demultiplexer 3245 receives the image data of the second resolutionfrom the resolution increasing unit 3244. The demultiplexer 3245 thenswitches an output destination of the image data of the secondresolution according to the signal indicating the position of the edgeregion that has been output from the edge detecting unit 3243.Specifically, the demultiplexer 3245 outputs pixels corresponding to aportion other than the edge region detected by the edge detecting unit3243 in the received image data of the first resolution to themultiplexer 3248 as it is. Moreover, the demultiplexer 3245 outputs thepixels corresponding to the edge region detected by the edge detectingunit 3243 in the received image data of the first resolution to thesmoothing unit 3247 as it is.

The smooth-pattern storage unit 3246 stores smooth patterns. The smoothpattern is a partial image of the second resolution (4800 dpi) thatexpresses a smoothed shape obtained by smoothing the stepped-shapeexpressed by an edge pattern.

The smoothing unit 3247 arranges a smooth pattern stored in thesmooth-pattern storage unit 3246 in a region corresponding to the edgeregion in the image data of the second resolution. That is, thesmoothing unit 3247 replaces respective pixels included in the regioncorresponding to the edge region in the image data of the secondresolution with pixels at corresponding positions included in the smoothpattern.

The multiplexer 3248 receives the pixels corresponding to the portionother than the edge region that are output from the resolutionincreasing unit 3244, and the pixels of the edge region that are outputfrom the smoothing unit 3247. The multiplexer 3248 then multiplexes thepixels corresponding to the portion other than the edge region that areoutput from the resolution increasing unit 3244, and the pixels of theedge region that are output from the smoothing unit 3247 according tothe signal indicating the position of the edge region output from theedge detecting unit 3243, to output them as one piece of image data ofthe second resolution.

The resolution converting unit 3231 having such a configuration canincrease the resolution to convert image data of the first resolutioninto image data of second resolution, and can smooth edges (smoothing)of lines in a parallel line pattern.

The line-region detecting unit 3241 and the edge detecting unit 3243acquire the image data of the first resolution, and detect the parallelline pattern region and the edge region. Thus, the line-region detectingunit 3241 and the edge detecting unit 3243 can detect the parallel linepattern region and the edge region with small processing amount.Alternatively, the line-region detecting unit 3241 and the edgedetecting unit 3243 may acquire image data of the second resolutionoutput from the resolution increasing unit 3244 to detect the parallelline pattern region and the edge region.

Moreover, the smoothing unit 3247 may smooth edges by performing aspatial filter operation on the image data of the second resolutionoutput from the resolution increasing unit 3244. Thereby, the resolutionconverting unit 3231 can smooth edges, without storing smooth patternsin advance.

FIG. 14 is a diagram showing a part of a parallel line pattern in imagedata of 1200 dpi. In following diagrams showing image data, a positionof each squared grid indicates a position of a pixel at correspondingresolution.

Lines forming a parallel line pattern are obliquely arranged relative toa direction of arrangement of pixels. Therefore, an edge of each linehas a stepped-shape that varies in width by one pixel distance or moreof the first resolution (1200 dpi) as shown in FIG. 14.

FIG. 15 is a diagram showing an example of an edge pattern and a smoothpattern to detect and smooth an upper edge of a line shown in FIG. 14.Furthermore, FIG. 16 is a diagram showing an example of an edge patternand a smooth pattern to detect and smooth a lower edge of the line shownin FIG. 14.

The edge-pattern storage unit 3242 stores the partial image of the firstresolution (1200 dpi) expressing a stepped-shape at an upper (or right)edge and a lower (or left) edge of a line as shown in FIG. 15(a) andFIG. 16(a), as an edge pattern. The edge detecting unit 3243 detects aregion that matches with such an edge pattern as an edge region from aparallel line pattern as shown in FIG. 14.

For example, edge patterns are registered by a user in advance.Moreover, edge patterns may be of any size. For example, although theedge pattern is a partial image of 3×2 pixels in the examples shown inFIG. 15(a) and FIG. 16(a), the number of pixels may be larger than this.Furthermore, more than one kind of edge pattern may be registered forone parallel line pattern.

Moreover, an edge pattern is an image expressing a stepped-shape thatvaries according to the angle of lines. An edge pattern shows differentstepped-shapes between when the angle of lines is 45 degrees relative tothe direction of arrangement of pixels and when the angle of lines is 60degrees relative to the direction of arrangement of pixels.

Moreover, the edge detecting unit 3243 may rotate an edge patternshowing the stepped-shape of an upper (or right) edge by 180 degrees togenerate an edge pattern showing the stepped-shape of a lower (or left)edge of a line, or may perform the opposite. Thus, the edge-patternstorage unit 3242 can reduce the number of edge patterns to be stored.

The smooth-pattern storage unit 3246 stores a partial image of thesecond resolution (4800 dpi) expressing a shape that is obtained bysmoothing a stepped-shape in a corresponding edge pattern as shown inFIG. 15(b) and FIG. 16(b), as a smooth pattern.

Smooth patterns are determined in advance corresponding to respectiveedge patterns. A smooth pattern is in a size corresponding to an edgepattern. For example, if an edge pattern is in a size of 3×2 pixels, asmooth pattern is to be a partial image in a size of 12×8 pixels, whichis the size having resolution four times as high as that of the size of3×2 pixels.

The smoothing unit 3247 arranges a smooth pattern in the regioncorresponding to the edge region that matches with the edge pattern inthe image data of the second resolution. More specifically, thesmoothing unit 3247 arranges the smooth pattern shown in FIG. 15(b) inthe region corresponding to the edge region that matches with the edgepattern shown in FIG. 15(a). Moreover, the smoothing unit 3247 arrangesthe smooth pattern shown in FIG. 16(b) in the region corresponding tothe edge region that matches with the edge pattern shown in FIG. 16(a).Thus, the smoothing unit 3247 can smooth each edge of lines in aparallel line pattern such that the distance between the edges opposedto each other in two adjacent lines is constant at any position onlines.

Moreover, in a smooth pattern, the number of pixels expressing a lineportion is identical to the number of pixels expressing the line whenthe edges are not smoothed. Thus, the smoothing unit 3247 can smootheach edge of lines of a parallel line pattern so as to cause the lightsource to emit light having the same energy as the energy of light thatis emitted from the light source based on the image data that has beenconverted into data of the second resolution without smoothing theedges.

FIG. 17 is a diagram showing a part of a parallel line pattern in imagedata of 4800 dpi after edges of the lines shown in FIG. 14 are smoothed.As shown in FIG. 17, the resolution converting unit 3231 can convert aparallel line pattern into higher resolution data having the secondresolution (4800 dpi), and can smooth each edge of lines drawn obliquelyrelative to the direction of arrangement of pixels. Thus, the resolutionconverting unit 3231 can make the edge of each line to vary smoothly byan interval of a pixel of the second resolution (4800 dpi).

As described above, the color printer 2000 according to the presentembodiment performs conversion from the first resolution (1200 dpi) tothe second resolution (4800 dpi) in the drive control unit 3103. Thus,the color printer 2000 enables to suppress the data transfer amount fromthe image processing unit 3102 to the drive control unit 3103.

In the color printer 2000, each edge of lines forming a parallel linepattern is smoothed at the time of conversion from the first resolutionto the second resolution. Thus, in the color printer 2000, intervalsbetween lines in electrostatic latent images that are formed on thephotosensitive drum 2030 corresponding to respective lines areapproximately constant at any position in the direction of extension ofthe lines. Accordingly, influence from an electrostatic latent image ofother lines is uniform, and therefore, it is possible to avoid tonerfrom adhering non-uniformly or avoid toner scattering between lines.Thus, according to the color printer 2000, a parallel line patternhaving uniform concentration can be printed.

(First Modification)

Next, a first modification of the embodiment is explained. The firstmodification has functions and components approximately identical tothose of the embodiment explained referring to FIG. 1 through FIG. 17,and therefore, the identical symbols are given to units havingapproximately identical functions and components, and explanationthereof is omitted except differences.

FIG. 18 is a configuration diagram of the resolution converting unit3231 according to the first modification. The resolution converting unit3231 according to the first modification receives object informationfrom the image processing unit 3102 together with image data. The objectinformation indicates the type of object being the source of the region(pixel) for each region (for example, for each pixel) of image data.

For example, if a corresponding pixel is a part of a character, anattribute indicating “character” is indicated in the object information.Moreover, if a corresponding pixel is a part of a figure, an attributeindicating “figure” is indicated in the object information. Furthermore,if a corresponding pixel is a part of a photograph, an attributeindicating “photograph” is indicated in the object information.

The line-region detecting unit 3241 detects a parallel line patternbased on the received object information. For example, the line-regiondetecting unit 3241 performs processing of detecting a parallel linepattern on the region for which the attribute of “photograph” isindicated in the object information and for which the parallel linedithering is possibly performed. On the contrary, the line-regiondetecting unit 3241 does not perform processing of detecting a parallelline pattern on the region for which the attribute of “character” or“figure” is indicated in the object information, and that has nopossibility that the parallel line dithering is performed. Thus, theline-region detecting unit 3241 can detect a parallel line patternefficiently and accurately.

(Second Modification)

Next, a second modification of the embodiment is explained. The secondmodification has functions and components approximately identical tothose of the embodiment explained referring to FIG. 1 through FIG. 17,and therefore, the identical symbols are given to units havingapproximately identical functions and components, and explanationthereof is omitted except differences.

FIG. 19 is a configuration diagram of the resolution converting unit3231 according to the second modification. The resolution convertingunit 3231 according to the second modification further includes an angledetecting unit 3250, an edge-pattern selecting unit 3251, and asmooth-pattern selecting unit 3252.

The angle detecting unit 3250 detects the angle of lines, which form aparallel line pattern, relative to the direction of arrangement ofpixels. The angle detecting unit 3250 detects the angle of lines bypattern matching, as an example. Moreover, the angle detecting unit 3250may acquire angle data of the parallel line pattern from the imageprocessing unit 3102 to detect the angle.

The edge-pattern storage unit 3242 stores various kinds of edge patternsthat express stepped-shapes corresponding to respective angles of linesforming a parallel line pattern. As one example, the edge-patternstorage unit 3242 stores an edge pattern expressing a stepped-shapecorresponding to an angle of 45 degrees, an edge pattern expressing astepped-shape corresponding to an angle larger than 0 degrees andsmaller than 45 degrees, and an edge pattern expressing a stepped-shapecorresponding to an angle larger than 45 degrees and smaller than 90degrees.

The edge-pattern selecting unit 3251 selects an edge patterncorresponding to the angle detected by the angle detecting unit 3250from the edge-pattern storage unit 3242, to supply it to the edgedetecting unit 3243. The edge detecting unit 3243 detects, in a parallelline pattern, an edge region that matches with the edge pattern selectedby the edge-pattern selecting unit 3251, by pattern matching.

The smooth-pattern storage unit 3246 stores various kinds of smoothpatterns that express smoothed stepped-shapes corresponding torespective angles of lines forming a parallel line pattern. As oneexample, the smooth-pattern storage unit 3246 stores a smooth patterncorresponding to an angle of 45 degrees, a smooth pattern correspondingto an angle larger than 0 degrees and smaller than 45 degrees, and asmooth pattern corresponding to an angle larger than 45 degrees andsmaller than 90 degrees.

The smooth-pattern selecting unit 3252 selects a smooth patterncorresponding to the angle detected by the angle detecting unit 3250from the smooth-pattern storage unit 3246, to supply it to the smoothingunit 3247. The smoothing unit 3247 arranges the smooth pattern that isselected by the smooth-pattern selecting unit 3252, in a regioncorresponding to the edge region in image data of the second resolution.

FIG. 20 is a diagram showing a part of a parallel line pattern of 1200dpi that is formed with 45-degree lines. FIG. 21 and FIG. 22 arediagrams showing an example of an edge pattern and a smooth patterncorresponding to the parallel line pattern that are formed with45-degree lines. FIG. 23 is a diagram showing a part of a parallel linepattern of 4800 dpi after edges of the parallel line pattern that isformed with 45-degree lines are smoothed.

The pseudo-halftone processing unit 3224 generates any of a parallelline pattern formed with 45-degree lines, a parallel line pattern formedwith approximately 30-degree lines, and a parallel line pattern formedwith approximately 60 degree-lines, as an example.

In this case, the parallel line pattern formed with 45-degree linestakes, for example, a form as shown in FIG. 20. Moreover, the parallelline pattern formed with approximately 30-degree lines takes, forexample, a form as shown in FIG. 14. The parallel line pattern formedwith approximately 60-degree lines takes, for example, a form that isobtained by horizontally reversing FIG. 14 after 90-degree rotationthereof.

Furthermore, the edge-pattern storage unit 3242 stores partial images asshown in FIG. 21(a) and FIG. 22(a) as edge patterns corresponding to a45-degree line, for example. The edge-pattern storage unit 3242 storespartial images as shown in FIG. 15(a) and FIG. 16(a) as edge patternscorresponding to an approximately 30-degree line. The edge-patternstorage unit 3242 stores partial images that are images shown in FIG.15(a) and FIG. 16(a) horizontally reversed after 90-degree rotationthereof as edge patterns corresponding to an approximately 60-degreeline.

Moreover, the smooth-pattern storage unit 3246 stores partial images asshown in FIG. 21(b) and FIG. 22(b) as smooth patterns corresponding tothe 45-degree line. The smooth-pattern storage unit 3246 stores partialimages as shown in FIG. 15(b) and FIG. 16(b) as smooth patternscorresponding to the approximately 30-degree line. The smooth-patternstorage unit 3246 stores partial images that are images shown in FIG.15(b) and FIG. 16(b) horizontally reversed after 90-degree rotationthereof, as smooth patterns corresponding to the approximately 60-degreeline.

By using such an edge pattern and a smooth pattern, the resolutionconverting unit 3231 can generate a parallel line pattern of 45-degreelines in which edges of the lines are smoothed as shown in FIG. 23.Moreover, the resolution converting unit 3231 can generate a parallelline pattern of approximately 30-degree lines in which edges of thelines are smoothed as shown in FIG. 17. Furthermore, the resolutionconverting unit 3231 can generate a parallel line pattern ofapproximately 60-degree lines in which edges of the lines are smoothed,as an image that is obtained by horizontally reversing the image shownin FIG. 17 after 90-degree rotation thereof.

The resolution converting unit 3231 as described can smooth edgesappropriately according to the angle of lines in a parallel line patternthat is generated by the pseudo-halftone processing unit 3224.

(Third Modification)

Next, a third modification of the embodiment is explained. The thirdmodification has functions and components approximately identical tothose of the embodiment explained referring to FIG. 1 through FIG. 17,and therefore, the identical symbols are given to units havingapproximately identical functions and components, and explanationthereof is omitted except differences.

FIG. 24 is a configuration diagram of the resolution converting unit3231 according to the third modification. The resolution converting unit3231 according to the third modification further includes acharacteristic detecting unit 3253 and a switch control unit 3254.

The characteristic detecting unit 3253 detects the number of lines perunit length or the density of lines forming a parallel line pattern. Thecharacteristic detecting unit 3253 detects the number of lines per unitlength or the density by pattern matching, as an example. Moreover, thecharacteristic detecting unit 3253 may acquire data of the number oflines per unit length and data of the density of a parallel line patternfrom the image processing unit 3102, to detect the number of lines perunit length or the density.

The switch control unit 3254 cancels arrangement of a smooth patterninto the image data of the second resolution when the number of linesper unit length or the density detected by the characteristic detectingunit 3253 is lower than a predetermined value. That is, even if aparallel line pattern is included, the switch control unit 3254 onlyperforms processing of converting into higher resolution by theresolution increasing unit 3244, and the smoothing processing is notperformed.

When an adjacent line to a line is close, the electric field intensityand the like of an electrostatic latent image of the line formed on thephotosensitive drum 2030 becomes unstable, receiving an influence fromthe electrostatic latent image of the adjacent line. However, when theadjacent line is separated by a certain distance or more, the influencefrom the electrostatic latent image of the adjacent line that isreceived by the electrostatic latent image of the line formed on thephotosensitive drum 2030 is small. Accordingly, when the number of linesper unit length or the density of the lines is lower than thepredetermined value, the concentration of the parallel line pattern doesnot become non-uniform, or toner scattering does not occur. Therefore,in the resolution converting unit 3231 according to the thirdmodification, the amount of processing can be reduced by cancellingarrangement of a smooth pattern when the concentration is notnon-uniform or when no toner scattering occurs.

(Fourth Modification)

Next, a fourth modification of the embodiment is explained. The fourthmodification has functions and components approximately identical tothose of the embodiment explained referring to FIG. 1 through FIG. 17,and therefore, the identical symbols are given to units havingapproximately identical functions and components, and explanationthereof is omitted except differences.

FIG. 25 is a diagram showing a part of a parallel line pattern of 1200dpi expressed by ternary pixel values. FIG. 26, FIG. 27, and FIG. 28 arediagrams showing an example of an edge pattern and a smooth patterncorresponding to the parallel line pattern expressed by ternary pixelvalues. FIG. 29 is a diagram showing a part of a parallel line patternof 4800 dpi expressed by ternary pixel values after edges therein aresmoothed.

The pseudo-halftone processing unit 3224 according to the fourthmodification generates a parallel line pattern in which pixel values areexpressed by ternary values. The pseudo-halftone processing unit 3224generates a parallel line pattern of the first resolution (1200 dpi)expressed by ternary pixel values as shown in FIG. 25, for example.

In FIG. 25, a pixel expressed in white indicates that the luminance oflight emitted from the light source 2200 is 0%, and a pixel expressed inblack indicates that the luminance of light emitted from the lightsource 2200 is 100%, and a pixel expressed in cross-hatching indicatesthat the luminance of light emitted from the light source 2200 is 50%.

In such a case, the edge-pattern storage unit 3242 stores a partialimage of the first resolution (1200 dpi) that expresses a stepped-shapeby ternary pixel values as shown in FIG. 26(a), FIG. 27(a), and FIG.28(a), as an edge pattern.

Moreover, the smooth-pattern storage unit 3246 stores a partial image ofthe second resolution (4800 dpi) that expresses a shape by binary pixelvalues as shown in FIG. 26(c), FIG. 27(c), and FIG. 28(c), as a smoothpattern.

The smooth pattern shown in FIG. 26(c) is a partial image that isgenerated by converting a partial image shown in FIG. 26(a) into a 1-bitpartial image of the second resolution of 4800 dpi to increaseresolution as shown in FIG. 26(b), and then by smoothing the partialimage so as to have equivalent energy. Moreover, the smooth patternshown in FIG. 27(c) is a partial image that is generated by converting apartial image shown in FIG. 27(a) into a 1-bit partial image of thesecond resolution of 4800 dpi to increase resolution as shown in FIG.27(b), and then by smoothing the partial image so as to have equivalentenergy. Furthermore, the smooth pattern shown in FIG. 28(c) is a partialimage that is generated by converting a partial image shown in FIG.28(a) into a 1-bit partial image of the second resolution of 4800 dpi toincrease resolution as shown in FIG. 28(b), and then by smoothing thepartial image so as to have equivalent energy.

By using such an edge pattern and a smooth pattern, the resolutionconverting unit 3231 can smooth edges as shown in FIG. 29 for a parallelline pattern that expresses a stepped-shape by ternary pixel values.

As described, the resolution converting unit 3231 according to thefourth modification can appropriately smooth edges even if pixel valuesin a parallel line pattern that is generated by the pseudo-halftoneprocessing unit 3224 are expressed by ternary or more values.

According to an embodiment, it is possible to make concentration of aparallel line pattern uniform without increasing a data transfer amountof image data.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. An image forming apparatus that forms an imageaccording to light emitted from a light source, comprising: circuitryconfigured to function as a pseudo-halftone processing unit thatprocesses input image data to output image data of first resolutionhaving a parallel line pattern; a resolution converting unit thatconverts the image data of the first resolution having the parallel linepattern into image data of second resolution that is higher than thefirst resolution; a modulation-signal generating unit that generates amodulation signal obtained by modulating the image data of the secondresolution according to a clock signal; and a light-source driving unitthat drives the light source according to the modulation signal, whereinthe pseudo-halftone processing unit converts a region of pixels havingthe same pixel value in the input image data into the parallel linepattern that is formed with a plurality of parallel lines obliquerelative to a direction of arrangement of pixels to expressconcentration by an area ratio, and the resolution converting unitsmooths each edge of the lines forming the parallel line pattern afterthe image data of the first resolution is converted into the image dataof the second resolution.
 2. The image forming apparatus according toclaim 1, wherein the pseudo-halftone processing unit converts the regionof pixels having the same pixel value in the input image data into theparallel line pattern formed with the lines having the area ratioaccording to the pixel value.
 3. The image forming apparatus accordingto claim 1, wherein the resolution converting unit smoothes each edge ofthe lines in the parallel line pattern such that a distance betweenedges opposed to each other in two adjacent lines is constant at anyposition on the lines.
 4. The image forming apparatus according to claim1, wherein the resolution converting unit smoothes each edge of thelines in the parallel line pattern so as to cause the light source toemit light having energy equivalent to energy of light emitted from thelight source according to the image data that has been converted intothe second resolution without smoothing edges.
 5. The image formingapparatus according to claim 1, wherein the resolution converting unitincludes circuitry configured as a line-region detecting unit thatdetects the parallel line pattern; an edge detecting unit that detectsan edge region that matches with an edge pattern expressing astepped-shape of an edge of a line of the first resolution from theparallel line pattern; a resolution increasing unit that converts imagedata of the first resolution into image data of the second resolution toincrease resolution; and a smoothing unit that arranges, in a regioncorresponding to the edge region in the image data of the secondresolution, a smooth pattern of the second resolution expressing a shapethat is obtained by smoothing the stepped-shape.
 6. The image formingapparatus according to claim 5, wherein the edge detecting unit detectsthe edge region by performing pattern matching on the parallel linepattern of the image data of the first resolution and the edge patternof the first resolution.
 7. The image forming apparatus according toclaim 5, wherein the line-region detecting unit acquires, for eachregion of the image data of the first resolution, object informationthat indicates a type of object being a source of the region, anddetects the parallel line pattern based on the acquired objectinformation.
 8. The image forming apparatus according to claim 5,wherein the resolution converting unit further includes circuitryconfigured as an angle detecting unit that detects an angle of the linesrelative to a direction of arrangement of pixels, and the edge detectingunit detects the edge region that matches with the edge patternexpressing the stepped-shape corresponding to the angle from theparallel line pattern by pattern matching, and the smoothing unitarranges a smooth pattern of the second resolution expressing a shapethat is obtained by smoothing the stepped-shape corresponding to theangle, in a region corresponding to the edge region in the image data ofthe second resolution.
 9. The image forming apparatus according to claim5, wherein the resolution converting unit further includes circuitryconfigured as a characteristic detecting unit that detects number of thelines per unit length or density of the lines, and a switch control unitthat cancels arrangement of the smooth pattern into the image data ofthe second resolution when the number or the density is smaller than apredetermined value.
 10. The image forming apparatus according to claim5, wherein the edge detecting unit detects the edge region by performingpattern matching on the parallel line pattern in image data of the firstresolution, in which pixel values are expressed by ternary or morevalues, and the edge pattern of the first resolution in which pixelvalues are expressed by ternary or more values.
 11. The image formingapparatus according to claim 1, wherein the light source is a verticalcavity surface emitting laser.
 12. An image forming method of forming animage according to light emitted from a light source, comprising:processing input image data to output image data of first resolutionhaving a parallel line pattern; converting the image data of the firstresolution having the parallel line pattern into image data of secondresolution that is higher than the first resolution; generating amodulation signal obtained by modulating the image data of the secondresolution according to a clock signal; and driving the light sourceaccording to the modulation signal, wherein at the processing the inputimage data, a region of pixels having the same pixel value in the inputimage data is converted into the parallel line pattern that is formedwith a plurality of parallel lines oblique relative to a direction ofarrangement of pixels to express concentration by an area ratio, and theconverting includes smoothing each edge of the lines forming theparallel line pattern after the image data of the first resolution isconverted into the image data of the second resolution.
 13. A method ofproducing a printed material, comprising: processing input image data tooutput image data of first resolution having a parallel line pattern;converting the image data of the first resolution having the parallelline pattern into image data of second resolution that is higher thanthe first resolution; generating a modulation signal obtained bymodulating the image data of the second resolution according to a clocksignal; forming, on a latent image carrier, an electrostatic latentimage by light emitted from a light source by driving the light sourceaccording to the modulation signal; making toner adhere to theelectrostatic latent image that is formed on the latent image carrier;and transferring the toner onto an object to produce a printed material,wherein at the processing the input image data, a region of pixelshaving the same pixel value in the input image data is converted intothe parallel line pattern that is formed with a plurality of parallellines oblique relative to a direction of arrangement of pixels toexpress concentration by an area ratio, and the converting includessmoothing each edge of the lines forming the parallel line pattern afterthe image data of the first resolution is converted into the image dataof the second resolution.